Java-自增和自减

n++,n-- 后缀，先赋值后运算。
++n,--n 前缀，先运算后赋值。

int m = 7;
int n = 7;
int a = 2 * ++m;  //a = 16,m = 8 
int b = 2 * n++;   //b = 14,n = 8